This study is designed to investigate the safety and tolerability of aerosolized INS365 in pediatric and adult cystic fibrosis patients with mild to moderate lung disease. The primary objectives are to evaluate the safety of INS365 and to determine the maximally tolerated dose, which will allow selection of a safe dose to administer in Phase II Trials. INS365, a triphosphate nucleotide, may be useful in patients with thickened airway secretions (like CF) because it may improve ciliary beat frequency and increase hydration in the airways, and therefore improve musociliary clearance.